Bernoulli distribution
Toss a coin, how likely it lands on heads (1) or tails (0)?
$$
p(k)=
\begin{cases}
p, & \text{if $k=1$,} \\
1-p, & \text{if $k=0$,} \\
0, & \text{otherwise.}
\end{cases}
\\[20pt]
\text{where $p$ is the probability the coin lands on heads.}
$$